jason-1 / envisat cross-calibration

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Jason-1/Envisat cross-calibration - 1 - Y. Faugere (CLS) J. Dorandeu (CLS) N. Picot (CNES) P. Femenias (ESA) Jason-1 / Envisat Cross-calibration

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Jason-1 / Envisat Cross-calibration. Y. Faugere (CLS) J. Dorandeu (CLS) N. Picot (CNES) P. Femenias (ESA). Introduction. Objective : to show the improvement of the consistency between Jason-1 and Envisat in the GDRb configuration Data used Envisat USO anomaly Performances at crossovers - PowerPoint PPT Presentation

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Jason-1/Envisat cross-calibration- 1 -

Y. Faugere (CLS)

J. Dorandeu (CLS)

N. Picot (CNES)

P. Femenias (ESA)

Jason-1 / Envisat Cross-calibration

Jason-1/Envisat cross-calibration- 2 -

Introduction

Objective: to show the improvement of the consistency between Jason-1 and Envisat in the GDRb configuration

• Data used

• Envisat USO anomaly

• Performances at crossovers

• Mean Sea Level trends

• Conclusion

Jason-1/Envisat cross-calibration- 3 -

EnvisatCurrent processing

Data used

9 ................................................40 41 … 46 ..…52

26 ............................................135 136………..178Jason-1Current processing

Main Jason-1 GDR b changes:New orbit configuration (EIGEN-CG03C)New retracking (MLE4)Geophysical corrections (MOG2D, tides, …)

Main Envisat GDR b changes:New orbit configuration (EIGEN-CG03C)New wind speed model + new SSB modelGeophysical corrections (MOG2D, tides, …)

GDR a GDR b• More than 4 years available

Updated correction on Jason-1:Geophysical corrections for cycle <136SSB compatible with new standards for cycle >136

Updated correction on Envisat:Geophysical corrections for cycle <41USO drift + USO anomaly correction

Jason-1/Envisat cross-calibration- 4 -

30 70480 650

Before correction After correctionSLA cycle 46

(cm)

Envisat USO anomaly• Since February 2006, Envisat Ra-2 data have been affected by a major

anomaly: the Ultra Stable Oscillator (USO) anomaly• The anomaly consists in a a change of frequency of the USO device: bias +

oscillating signal at the orbital period• Translated into range, the impact is a ~5.5m bias + 30 cm of amplitude orbital

signal

• A temporary correction is proposed by ESA: Auxiliary files are distributed for each products: FDGDR, IGDR, GDR.

Jason-1/Envisat cross-calibration- 5 -

Envisat USO anomaly

February 2006

• 2 sets of USO correction are available for Ra-2 Envisat data:

September 2005

USO DRIFT onlyHas to be updated by

the user

USO DRIFT onlyIncluded in the

product

More informations on http://earth.esa.int/pcs/envisat/ra2/auxdata/

USO DRIFT + anomalyHas to be updated by the user

Jason-1/Envisat cross-calibration- 6 -

Performances at crossovers• EN/J1 10-day dual crossovers differences: methodology

grid cycle 31

grid cycle 32

.

.

.

grid cycle 40

Cyclic mean differences in 2°x2° boxes year 2005

Cyclic mean differences in 2°x2° boxes year 2006

grid cycle 41

grid cycle 42

.

.

.

grid cycle 50

Mean 31-40

stdev 31-40

Mean 41-50

stdev 41-50

=>systematic differences

=>time varying differences

!

•Model wet tropo used

Jason-1/Envisat cross-calibration- 7 -

Performances at crossovers• EN/J1 10-day dual crossovers differences: systematic differences

-3 3 -3 3

EN-J1 mean (cycles 31-40)

GDR A products

EN-J1 mean (cycles 41-50)

GDR B products + SSB compatible with the new standards

(cm) (cm)• Reduction of the geographically correlated systematic differences • A residual East/West signal is noticed

Jason-1/Envisat cross-calibration- 8 -

0 3

• EN/J1 10-day dual crossovers differences: time varying differences

0 3(cm) (cm)

• Strong reduction of the time varying differences • residual signal in North-West Atlantic, Indonesia

EN-J1 stdev (cycles 31-40)

GDR A products

EN-J1 stdev (cycles 41-50)

GDR B products + SSB compatible with the new standards

Performances at crossovers

Jason-1/Envisat cross-calibration- 9 -

Performances at crossovers

• Envisat and Jason-1 performances cross comparison at single 10-day crossover

Mean Standard deviation

Similar performances for the two missions

Selection on Latitude (<50°) bathymetry (<-1000 m) variability (<20cm)

Annual signal on Envisat

February 2006

Jason-1/Envisat cross-calibration- 10 -

Jason-1 and Envisat Mean Sea Level trends

• The EN and J1 MSL trend over the 4 years are not consistent

Jason-1

Envisat

Selection on latitude (<66°), seasonal signals removed Model wet tropo used

Jason-1/Envisat cross-calibration- 11 -

Jason-1 and Envisat Mean Sea Level trends

• The EN and J1 MSL trend over the 4 years are not consistent

• However the EN and J1 MSL trend are consistent over 2004-2005 period

Selection on Latitude (<66°), seasonal signals removed Model wet tropo used

Jason-1

Envisat

Consistent Not consistentNot consistent

Jason-1/Envisat cross-calibration- 12 -

Conclusion• The geographical differences between Envisat and jason-1 are strongly reduced by:

– the new geophysical corrections, – the use of Grace gravity fields in the orbit calculation– A new Jason-1 SSB compatible with the new standards (not in the product yet).

• Slight geographically correlated errors still remain. Longer time series in the new version are needed for fine investigation of the residual differences

• The performances of both Jason-1 and Envisat are good and similar. The USO anomaly correction allows Envisat Ra-2 data to recover their nominal quality

• The Envisat Mean Sea Level is inconsistent with the other altimeters at global and local scale.

• Cross-calibration against EnviSat is crucial:– For the Jason-1 performance assessment: In the context of only two precise altimeter missions flying

together (T/P is no more there!)– For preparing the Jason-2 launch: 3rd point of comparison to secure the cross-calibration exercise– Also requires further efforts on EnviSat long term performance (stability)

• More results: Poster Cyclic and yearly reports http://www.aviso.oceanobs.com/html/donnees/calval/